Submerged arc welding is a fully mechanised welding method characterised by high productivity and quality, often used for longer welding seems in thicker materials. During submerged arc welding one or more sequentially arranged welding electrodes melt in arcs.
The weld, particularly the melted material and the arc, are protected beneath a layer of pulverised flux. The flux melts in part during the process, thus creating a protecting layer of slag on the weld pool. The electrical current used in the process is relatively high, usually within 300-1500 Ampere per electrode. The electrodes used in submerged arc welding are usually 2.5-6 mm in diameter.
Fluxes used in submerged arc welding are granular fusible minerals typically containing oxides of manganese, silicon, titanium, aluminum, calcium, zirconium, magnesium and other compounds such as calcium fluoride. The flux is specially formulated to be compatible with a given electrode wire type so that the combination of flux and wire yields desired mechanical properties. All fluxes react with the weld pool to produce the weld metal chemical composition and mechanical properties. It is common practice to refer to fluxes as ‘active’ if they add manganese and silicon to the weld, the amount of manganese and silicon added is influenced by the arc voltage and the welding current level.
To find the highest productivity possible with submerged arc welding, with increased competitiveness as one result, one strives for increased weld speed and the highest possible deposition rate, i.e. melted welding consumables, or really created joint material, per hour and electrode.
One solution to this known in the art is to use multiple electrodes, positioned sequentially in the direction of the weld seem. Usually 2-3 electrodes are used, however, usage of up to 6 electrodes is known.
It is known that addition of metal which melts without an arc can improve the deposition rate during welding. For instance, metal powder or metal wires can be added during arc welding.
GB 1400051 A discloses an arrangement to improve the deposition rate during submerged arc welding of a workpiece 10. The general principle is illustrated in FIG. 1. Three continuously fed wire electrodes 30, 36, 40 serially disposed along a weld seam are consumed in arcs while moving in a welding direction 20. The electrodes 30, 36, 40 are also known as “hot” or “hot wire” electrodes. Two additional electrodes 32, 38 consumed without forming arcs are continuously fed into the molten weld pool 12 in the region of the arc of the middle electrode 36. These additional electrodes 32, 38, also known as “cold wires” or “cold wire electrodes” are in continuous short-circuit contact with the weld pool 12. The two electrodes 32, 38 consumed in the molten weld pool 12 without the formation of arcs are melted by resistance heating as well as by the heat generated by the middle electrode 36. The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool 12. An additional shielding gas is not required. Prior to welding, a thin layer of flux powder is placed on the workpiece surface. The arc moves along a joint line in welding direction 20 and as it does so, flux is fed to the welding area by a flux feed hopper. As the arc is completely covered by the flux layer, heat loss is extremely low. This produces a thermal efficiency as high as 60%, compared with 25% for manual metal arc. There is no visible arc light, welding is virtually spatter-free and there is no need for fume extraction.
Even though the above mentioned solutions increase the deposition rate during welding it is desirable to provide a better handling of such cold electrodes.